1. Field of the Invention
The present invention relates to a process for oxidizing keto groups pendant to a polymer chain to oxycarbonyl moieties. More particularly, the invention involves a process whereby pendant keto groups present in polymers obtained by polymerizing .alpha.,.beta.-unsaturated ketones are oxidatively converted to oxycarbonyl groups.
2. Description of the Prior Art
The ability to chemically introduce sensitizing groups, such as ketonic moieties which absorb radiation in the region produced by natural sunlight, to impart some degree of photodegradability to polymer systems is known. This is accomplished by copolymerizing a monomer containing the sensitizing group with one or more other monomers. The sensitizing groups provide sites within the polymer molecule which are susceptible to attack and where the polymer chain will be broken. Breaking the polymer chain reduces the molecular weight and forms smaller segments which facilitates further degradation in that the polymer surface area is increased and more and different chain ends are produced. When the polymer chain is broken in enough places, it then also becomes susceptible to degradation by biological mechanisms--ultimately to CO.sub.2 and water. The incorporation of sensitizing groups to develop photodegradable plastics and commercial plastic materials produced using this approach arc discussed by J. Guillet in Proceedings of Symposium on Degradable Plastics, The Society of the Plastics Industry, Inc., Washington, D.C., June 10, 1987.
Homopolymers and copolymers which contain sensitizing groups obtained by the polymerization of .alpha.,.beta.-unsaturated ketones and generically referred to as vinyl ketone polymers are known. A general review of vinyl ketone polymers and the various methods employed for their polymerization is provided in Encyclopedia of Polymer Science and Technology, Vol. 14, 617-636, Interscience, a division of John Wiley & Sons, New York, (1971).
While numerous carbonyl group-containing monomers have been homopolymerized, poly(methyl vinyl ketone) and poly (isopropenyl methyl ketone) are the most widely known vinyl ketone homopolymers. Copolymers of .alpha.,.beta.-unsaturated ketones with most of the common vinyl and diene monomers are also known. For example, numerous references cite copolymers of methyl vinyl ketone or isopropenyl methyl ketone with ethylene, styrene, butadiene, butyl acrylate and vinylidene chloride. Photodegradable polymers obtained by copolymerizing vinyl ketones with various comonomers and uses of such polymers are disclosed in U.S. Pat. Nos. 3,753,952, 3,811,931, 3,853,814, 3,860,538 and 3,878,169. Terpolymers prepared from the following monomers are also known: methyl vinyl ketone, styrene and acrylonitrile; methyl vinyl ketone, styrene and methyl methacrylate; methyl vinyl ketone, styrene and acrylic acid; and methyl vinyl ketone, methacrylonitrile and vinyltoluene.
Polymers containing keto groups in the polymer chain and terminal ester groups have been produced by the palladium(II) catalyzed copolymerization of carbon monoxide with ethylene in alcoholic solvents as disclosed by T. Lai, et al in Organometallics, 3, 866-870(1984). The amount of ester functionality is obviously limited using this approach.
It is also possible in copolymerizations of keto-containing monomers to include one or more comonomers containg ester functionality, such as vinyl acetate and alkyl acrylates or methacrylates. Due to the different reactivities of the various monomers, however, problems can be encountered using this approach.
It would be advantageous if ester groups could be introduced into vinyl ketone polymers without the need to include ester-containing monomers in the polymerization, such as by post-polymerization modification of the polymer.
U.S. Pat. Nos. 4,929,711 and 4,957,997 disclose an oxidation process for converting polyketones, i.e., polymers having carbonyl groups within the polymer backbone, to polyesters. Organic peroxyacid oxidizing agents are used for these processes. Pending application Ser. No. 498,527 discloses poly(keto-esters) produced by the foregoing processes comprised of carbonyl units, oxycarbonyl units and linking units derived from olefinic monomers.